RFID tag designs and sensors are disclosed that include a dispersive antenna and exhibit greater detection ranges relative to conventional designs. The designs include, for example a transponder having including a rectifier, a radio-frequency identification (RFID) circuit for receiving and responding to interrogation signals, and a frequency dispersion element for receiving a multi-phase input signal and creating a pulse therefrom for input to the rectifier. Frequency-dispersive elements (e.g., antennas) and compatible interrogation waveforms can be used so that the rectifying diodes receive high peak voltage levels relative to the average voltage levels.